Top down prefrontal affective modulation of tinnitus with multiple sessions of tDCS of dorsolateral prefrontal cortex

Most forms of tinnitus are attributable to reorganization and hyperactivity in the auditory central nervous system with coactivation of nonauditory brain structures. One such nonauditory brain area is the dorsolateral prefrontal cortex (DLPFC), which is important for the integration of sensory and emotional aspects of tinnitus. Based on extensive evidence that transcranial direct current stimulation can induce significant effects on DLPFC-related cognitive function, we aimed to investigate whether left or right anodal DLFPC tDCS is associated with modulation of tinnitus. We conducted a double-blind, placebo-controlled cross-over study in which 15 subjects with tinnitus were randomly assigned to receive active and sham anodal tDCS over left (n = 8) or right DLPFC (n = 7) for six sessions in a counterbalanced order; the cathode electrode was placed in the contralateral DLPFC. The results demonstrate that both active conditions-irrespective of the anodal position-can decrease tinnitus annoyance but it is not associated with improvements in tinnitus intensity when comparing pre-tDCS versus post-tDCS as well as comparing sham-tDCS versus real tDCS. Also, we show that the anode electrode placed over the left DLPFC modulates depression when comparing pre-tDCS versus post-tDCS as well as comparing sham-tDCS versus real tDCS. In addition, we also show that the anode electrode placed over the right DLPFC modulates anxiety when comparing pre-tDCS versus post-tDCS. This latter effect does not remain when we compare sham-tDCS versus real tDCS. This study further supports the involvement of the prefrontal cortex in the neural network associated with tinnitus, and also provides initial evidence for a potential brain stimulation site for tinnitus treatment in association with other treatments that can reduce tinnitus intensity.